Device for injection by top-blowing into a metal bath

ABSTRACT

IN REFINING A FERROUS MELT IN A METALLURGICAL FURNACE, A PRIMARY STREAM OF OXIDIZING FLUIS IS TRAINED UPON THE BATH SURFACE FROM A LANCE WHICH ALSO HAS MEANS FOR EMITTING A SECONDARY STREAM OF OXIDIZING FLUID, THE LATTER ENVELOPING THE PRIMARY STREAM AND SWIRLING AROUND IT, WITH OR WITHOUT INJECTION OF SOLID PARTICLES ENTRAINED BY THE PRIMARY STREAM.

March 2, 1971 R. MERCATORIS L DEVICE FOR INJECTION BY TOP-BLOWING INTOA-METAL BATH Filed 001;. 2, 196? 2 Sheets-Sheet 1 Robert MercarorisJoseph Nepper Attorney March 2, 1971 DEVICE FOR INJECTION BY TOP-BLOWINGINTO A METAL BATH 2 Sheets-Sheet l Robert Mercaforis Joseph NepperINVENTORS.

BY Rm Attomy United States Patent 0 Int. (1621c 7/00 US. Cl. 266-34 9Claims ABSTRACT OF THE DISCLOSURE In refining a ferrous melt in ametallurgical furnace, a primary stream of oxidizing fluid is trainedupon the bath surface from a lance which also has means for emitting asecondary stream of oxidizing fluid, the latter enveloping the primarystream and swirling around it, with or without injection of solidparticles entrained by the primary stream.

Our present invention relates to a device for the treat ment of a metalbath in a metallurgical furnace (converter) by top-blowing of anoxidizing fluid, usually a gas or a gas mixture, which may entrain asuspended charge of pulverulent or granular solid material such as iron,alloying metals, lime or other reagents, e.g., as described in commonlyowned US. Pat. No. 3,130,252, issued Apr. 21, 1964, to Paul Metz.

In refining by top-blowing, i.e. injection from above of an oxidizingfluid (consisting in most cases of pure oxygen) which may be chargedwith particulate solids, it is very important that the width of thestream should be adjustable according to changing requirements duringdifferent phases of the refining operation. In the case, for example, ofa treatment of phosphorus-rich pig iron by means of oxygen blown fromabove, it is desirable to blow at the beginning of the operation with awidely spread stream, whereas after the initiation of sufl'lcientfoaming of the bath it is convenient to continue the blowing action witha more concentrated and more penetrating flow. Toward the end of therefining operation, depending on the actual conditions, it may beadvantageous to blow either with a narrow or with a broad stream.

It is known to realize such variations of jet width by the use of two ormore lances having different characteristics or by the use of only onelance while modifying the pressure of the injected gas and varying thedistance of the lance from the bath surface. It is also possible tocombine the two measures during operation. However, these prior blowingmethods are not fully satisfactory and do not allow easy and rapidvariation of the spread and depth of penetration of the oxygen flow.

In the aforementioned Metz patent there is described a simpler and moreefficient system designed to adjust spread in a manner suitable for agood control of the refining operation. This is accomplished with theaid of a lance including a central bore for the discharge of a primaryfluid stream and an annular passage which coaxially surrounds that boreand, through an array of connecting channels at the bottom of thepassage, directs a secondary fluid stream into a discharge port ornozzle where the two fluids are comingled. When the secondary stream isturned on, the spread of the overall flow is increased so that theoxidizing fluid is distributed under a relatively light pressure over alarge portion of the melt surface to cause intense slag foaming andconcomitant dephosphorization, along with the conversion of escaping COinto CO which 3,567,202 Patented Mar. 2, 1971 is an exothermic reactionand increases the consumption of scrap iron or grapeshot. As furtherexplained in the above patent, however, there are instancesparticularlyduring the later stages of refining operations-when it is advantageousto reduce the depth of penetration of the fluid into the bath, therebyachieving more effective decarburization; for this purpose the secondaryfluid stream is cut off so that the primary or central stream aloneimpinges upon the melt.

The general object of our present invention is to provide a blowingdevice representing a further advance of the art, and an improvementover the disclosure of that earlier patent.

A more particular object of our invention is to provide an easilyassembled lance capable of discharging two independently controllablegas streams in peripherally interacting relationship.

The blowing device according to the present invention is constituted bya cooled double lance comprising a generally upright central conduit forthe injection of a refining gas, capable of entraining suspended solidsto be added to the melt, and an outer conduit concentrically surroundingthe former to serve for the injection of secondary oxygen. The centralconduit is formed by an elongate, preferably converging-divergingtubular member. The outer conduit terminates at its bottom part in aperipheral array of generally helical channels which interconnect thetwo conduits and whose axes are skew to the conduit axis. Thisorientation of their axes increases the path length through the channelssufficiently to give guidance and direction to the outflowing jets ofsecondary oxygen even after they have left the discharge part. Theorientation of these jets is such that the secondary flow comes onlytangentially into contact with the main or central stream and surroundsit with a more or less gyratory movement completely enveloping the mainjet. The cross section of the secondary discharge channels, i.e., thesection transverse to the channel axis, has approximately the form of asemicircle open toward the outside. Thus, the secondary-flow channelscan be machined from the outside into a metallic collar constituting thelower extremity of the lance, with considerable simplification of themanufacture thereof.

Since the invention allows the secondary-flow channels to be machinedrather than bored or drilled, their direction (e.g., as defined by theangle included between the channel axis and a plane perpendicular to theconduit axis) can be chosen in accordance with the desired length of thechannel path. The aforementioned angle may range between about 35 and60.

The cross section of the secondary-flow channels can be either constant,so that each channel will have the form of a semicylinder, or varying,e.g., to form convergentdivergent passages as described in the earlierMetz patent.

The secondary oxygen jets leaving the channels can form a dense andprotective secondary-oxygen envelope along the inner nozzle wall. Tothis end, according to another feature of the invention, the crosssection of the discharge port increases abruptly at the exit of thecentral or main conduit in such a fashion as to create around the mainoxygen stream an annular void into whose upper part the secondarychannels discharge, the width of this void decreasing in the downwarddirection. Thus, the secondary-oxygen jets leaving the sloping channelsin the direction of the nozzle outlet combine to form within the nozzlea protective oxygen sheath free from entrained solid particles. As aresult, the primary oxygen stream charged with the solid particles doesnot come into contact with the inner nozzle wall so that the latter willnot be exposed to any wear by these solids. This means a considerableincrease in the life of the nozzle as compared with conventionalstructures.

The inclination of the channels of the outer conduit causes thesecondary-oxygen stream, on leaving the nozzle, to swirl around the mainstream without interacting therewith to any substantial extent, thence,the two injection streams will keep their individual functions while thecontrol of only one stream, i.e., the secondary oxygen stream, will besufficient to vary the spread of the flow striking the bath surface.

The main oxygen stream, serving primarily for the decarburization of themetal bath by agitating same, can be maintained effective during almostthe entire treat ment or until the desired carbon content is reached.Concurrently therewith and independently of the main stream. thesecondary stream can oxidize a large surface of the bath and/or of theslag, by virtue of its wide spread. It can thus be used, throughsuitable adjustment of its discharge rate, to accelerate thedephosphorization at any time and for any desired period. A lanceaccording to our invention offers, accordingly, the important technicaladvantage of yielding at the end of the refinement a lowphosphorus metalbath that may still retain high residual carbon content. This isnecessary or at least highly desirable in the manufacture of high-carbonsteels, especially if the starting material is a phosphorus-rich castiron.

Since the novel geometry of the secondary channels greatly increases theefiiciency of the secondary oxygen stream, its discharge rate can bereduced to just a fraction of that necessary with conventional lances.It therefore becomes possible to decrease the cross section of thesecondary conduit and of its oxygen-supply tubes as well as the size ofassociated metering and flow-control equipment.

Another advantageous aspect of the invention resides in the possibilityof maintaining the lance throughout the metallurgical operation at asubstantially constant distance from the bath surface. Moreover, thelance can be positioned nearer to the bath surface than heretoforeinasmuch as the desired spread of the oxygen flow can be realized at anyinstant by adjustment of the secondary stream without the necessity ofincreasing the nozzle distance from the melt. This is furtherfacilitated by the fact that the absence of substantial interactionbetween the two streams allows the secondary stream to retain virtuallyits entire kinetic energy as well as its direction of flow so as to beable to spread freely and widely across the melt.

The spreading out of the oxygen flow and the presence of an envelopingsheath of secondary oxidizing fluid lead to a considerable increase ofthe proportion of CO burned to CO inside the converter and therefore tothe fusion of a larger quantity of grapeshot.

The efiicient spreading of the oxidizing stream further promotes, veryadvantageously, the formation of a fluid slag layer from the beginningof the blowing operation, such layer preventing the ejection of metallicparticles and thereby reducing the loss of metal which generally occursin the early stages in the absence of a fluid slag.

A further advantage of the invention resides in the fact that, since thelance can be lowered more deeply into the converter, the zone of therefractory furnace lining subject to attack by the oxidizing fluid isreduced.

The preferred construction of a lance according to the invention offersother important technical advantages. Its axial conduits other than theoutermost tube terminate at the bottom in slidably guided ends in such aWay that all the tubes of the lance can relatively expand in thelongitudinal direction. This increases the useful life of the device bysuppressing any thermal stresses that might otherwise result in adeformation of the tubes or a throttling of the water passage situatedat the bottom of the cooling jacket in the region of the nozzle.

The invention will be described in gerater detail with reference to theaccompanying drawing in which:

FIG. 1 is a cross-sectional view of a lance embodying our invention; and

FIG. 2 is a cross-sectional view taken on the line II-II of FIG. 1.

The lance shown in the drawing comprises a central tube 1 with acylindrical main portion 11, a downwardly converging frustoconicalentrance portion 13 and a downwardly diverging exit portion 12, thelatter being constituted by a separate collar threadedly or otherwisereceived in a recess 14 at the lower end of cylinder 11. An outer shell2 coaxially surrounds the tube 1 and defines therewith an annularpassage 15 which terminates at its bottom in a peripheral array ofgenerally helicoidal connecting channels 3, the axes A of these channelslying skew to the common axis B of tube 1 and shell 2. Channels 3 aremilled into the outer periphery of collar 12 and, as here shown, are ofdownwardly divergent cross section; they open at the lower face 12a ofmember 12 into a discharge port 4 which is bounded by the innerperipheral surface 5 of an annular nozzle 16 integral with an outer ring6, the latter merging into an extension 17' of a cooling jacket 17 whichsurrounds the shell 2 to define channels 9, 10 for the circulation of acooling fluid. Elements 17, 17' and 6 are joined together by annularwelding seams 8 and 8; prior to complete assembly, the absence ofextension 17' gives access to a set of screws 18 by which a skirt 19 isfixed to shell 2 through the intermediary of nuts 20 welded onto theshell. A peripheral array of spacers 21 similarly connects an annularpartition 22, separating the conduits 9 and 10, to a cylindrical upwardextension 2' of shell 2. Packing rings 7, 7', 7" are provided along thecontact surfaces of the interfitting parts which, as shown, are allcentered on the same axis B for ease of assembly and disassembly.

Although the axes A of channel 3 seem to converge in FIG. 1 toward thecentral axis B, a reference to FIG. 2 reveals that these axes (asparticularly illustrated for axis A of channel 3') do not cross the axisB but pass it at a distance r which in FIG. 1 is seen to represent thereal axis of a one-sheet hyperboloid H centered on axis B, the curvatureof surface 5 substantially conforming to this hyperboloid; theaforementioned axis A is one of the asymptotes, intersecting at a point0 below the level of the discharge end of tube '1 but within the port 4.These asymptotes include with the horizontal (thus with a planetransverse to axis B) an angle a which may range within the aforestatedlimits and is here shown to equal about 60. It will be seen that anextension G of any generatrix of the frustoconical inner surface ofcollar 12 is tangent to the hyperboloid wall surface 5 of discharge port4 defined by the nozzle 16. Since the character of surface 5 exceeds theinner diameter of collar 12 at the level of face 12a, the port 4 forms adownwardly tapering annular space S around the central region occupiedby the primary fluid stream which issues from collar 12.

Owing to this construction, a stream of gaseous oxygen or otheroxidizing fluid passes substantially unhindered through outlet 4, evenin the presence of a secondary flow through annular passage 15, afterleaving the central tube 1 by way of collar 12; this primary fluidstream may be charged with particulate solid matter which, especiallyduring existence of an enveloping secondary flow, will be kept out ofcontact with the inner wall surface 5 of the nozzle.

The use of a separate nozzle member 16, with reinforced walls, affordsgreater wear resistance in the region of greatest thermal and mechanicalstress. If the nozzle needs replacement, the lance need to be cut andsubsequently rewelded only along the seam 8'; in the same way it is alsopossible to extract the collar 12 for replacement or repair.

Naturally, details of the construction described and illustrated may bemodified without departing from the spirit and scope of our invention.

We claim:

1. A lance for training an oxidizing fluid upon a ferrous melt,comprising a generally upright elongate tubular body forming a centralpassage for a primary fluid stream, a shell coaxially surrounding saidtubular body and forming therewith an annular passage for a secondaryfluid stream, said shell extending downwardly beyond said tubular bodyand forming a common discharge port for said streams, and a perforatedannular member at the bottom of said annular passage forming a pluralityof channels peripherally arrayed about the lower end of the common axisof said body and said shell and which include an angle betweensubstantially 35 and 60 with a plane perpendicular to the common axis ofsaid body and said shell, the axes of said channels substantiallycoinciding with generatrices of a one-sheet hyperboloid centered on saidcommon axis and having its waist within said discharge port, theperipheral surface of said discharge port having a curvatureapproximating the configuration of said one-sheet hyperboloid.

2. A lance as defined in claim 1, further comprising a cooling jacketsurrounding said shell.

3. A lance as defined in claim 2 wherein the inner wall surface of saidtubular body at the lower end thereof is a downwardly divergingfrustocone Whose extended generatrices are substantially tangent to theperipheral surface of said discharge port.

4. A lance as defined in claim 2 wherein said discharge port is formedby an annular nozzle fitted into the down wardly projecting end of saidshell.

5. A lance as defined in claim 4, further comprising a cooling jacketsurrounding said shell and a cylindrical partition within said jacket,said nozzle being integral with an outer ring adjoining said jacket andreceiving the lower end of said partition.

6. A lance as defined in claim 4 wherein said annular member comprises acollar with peripheral indentations of substantially semicircularcross-section forming said channels, the latter being externally boundedby an inner wall surface of said nozzle.

7. A lance as defined in claim 6 wherein said collar 6 has a neckreceived in an inner recess of said tubular body.

8. A lance for the top-blowing of a ferrous melt, comprising a generallyupright elongated tubular body forming a central passage for a primaryfluid stream; a shell coaxially surrounding said tubular body andforming therewith an annular passage for a secondary fluid stream; meansdefining a downwardly convergent frustoconical chamber forming a commondischarge port for said extremes; and a perforated annular member at thebottom of said annular passage forming a plurality of channelsperipherally arrayed about the lower end of the common axis of said bodyand said shell, said channels being each of semicircular cross sectionand including an angle of 35 to with a plane perpendicular to the commonaxis of said body and said shell, said channels being further inclinedin a common sense to respective axial planes.

9. The lance defined in claim 8 wherein said discharge port is formed byan annular nozzle fitted into an end of said shell projecting downwardlybeyond said tubular body, said channels being formed in a collar withperipheral indentations of substantially semicircular cross section andbeing externally bounded by an inner wall surface of said nozzle, saidcollar having a neck received in an inner recess of said tubular body.

References Cited UNITED STATES PATENTS 3,043,577 7/1962 Berry. 3,078,0842/1963 Foresi et al. -52X 3,202,201 8/1965 Masella et al 239-13233,239,205 3/1966 Metz 266-34 3,241,825 3/1966 Jilek et al. 266-343,317,309 5/1967 Rinesch 75-51X I. SPENCER OVERHOLSER, Primary ExaminerJ. S. BROWN, Assistant Examiner US. Cl. X.R. 75-51, 60; 239-497

